Much attention is paid to organic electroluminescent devices usable for flat panel display devices. Specifically, the organic electroluminescent devices are promising as inexpensive, solid-emission-type, large-emission-area, full-color display devices and writing light source arrays, and their development has been actively conducted. The organic light-emitting device generally comprises a couple of electrodes (a transparent electrode and a rear-surface electrode), and one or more organic layers containing a light-emitting layer formed between the electrodes. When an electric field is applied to the electrodes, electrons are injected into the light-emitting layer from one electrode, while holes are injected thereinto from the other electrode. With electrons and holes recombined in the light-emitting layer, energy is emitted as light when an energy level is lowered from a conduction band to a valence band.
WO 00/41893 discloses a method for thermally transferring an organic layer and a photo-thermal conversion layer onto a substrate by a laser beam by using a donor sheet having the organic layer and the photo-thermal conversion layer. However, such a thermal transfer method is disadvantageous in that a gas often penetrates into the interface between the organic layer and the substrate. The light-emitting efficiency, durability, and emission uniformity of the organic electroluminescent device depend on the conditions of the interface. Thus, an organic electroluminescent device produced by this method shows poor light-emitting properties when a gas penetrates into the interface.
In the case of transferring an organic layer from a donor onto a substrate by thermal writing in a predetermined pattern using a thermal head or a laser common in printing technologies, a temperature distribution generated around the organic layer pattern due to thermal diffusion blurs the pattern outline, failing to cut the pattern from the donor accurately. Thus, organic electroluminescent devices produced by the method are uneven in light emission and likely to suffer from poor durability, because of insufficient electric connection and the breakage of the organic layer. Further, yield is likely to be low because of low-accuracy positioning of the substrate and the thermal head or laser beam.
As methods of forming a patterned organic layer, relief dyeing methods, pigment dispersion methods, electrodeposition methods, vacuum deposition methods, ink-jet methods, and offset printing methods have been proposed. The relief dyeing methods comprise the steps of forming a predetermined pattern of a photoresist on an organic layer, and soaking a substrate having the organic layer in a dye solution. In the pigment dispersion methods, a pigment is dispersed in a photoresist, applied onto a substrate, exposed, and developed to form a pattern. In the electrodeposition methods, a predetermined pattern is formed on an electrode by electrodeposition. In the case of forming patterned organic layers containing different-color-emitting materials on a substrate in these methods, the different-color layers are formed by repeating the steps. The methods are thus costly and unsuitable for mass production.
In a case where a large-area, organic electroluminescent device is produced by a vacuum deposition method, which comprises disposing a mask between an organic layer and a deposition source to thermally deposit a light-emitting material in a pattern, the mask is likely to be deformed by heating. Further, the mask needs to be washed in vacuum, or to be separated, washed, and then placed under vacuum again, whereby the method is unsuitable for mass production. In the ink-jet methods and the offset printing methods, it is difficult to select solvents for stacking organic layers containing the light-emitting materials, and the stacked organic layers are mixed at the interfaces to reduce the light-emitting efficiency and the durability of the organic electroluminescent device.